Field of the Invention
The present invention relates to a sheet feeder that feeds a sheet set on a sheet supply tray to a processing section.
Description of the Related Art
An image forming device such as a copier or a scanner is provided with a sheet feeder for automatically feeding a sheet (document) onto a platen glass of an image reading section, which is called an ADF (Auto Document Feeder).
Conventionally, an ADF of this type is provided with a plurality of detection sensors for detecting a document position or a document set state. These detection sensors detect whether or not a document is present or whether or not a set document can be conveyed.
In the invention disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2005-244798, even if a document is set at a position where one of document set sensors does not detect the document, it is determined that the document is present when any one of the other sensors provided on the ADF indicates a detection state and thus conveyance of a subsequent document to the image reading section is restricted. In such a case, information for confirmation of the document set state is issued.
Further, in the invention disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2008-280153, the document set state is determined by means of a plurality of sensors provided on the ADF, and when a leading end of a document does not reach an aligning position at which the document can be fed and thus the document cannot actually be fed, an aligning means is used to align the document to the aligning position.
In a device as disclosed in above Jpn. Pat. Appln. Laid-Open Publication No. 2005-244798, there may be a case where it appears to an operator side that the document is properly set even though the set sensor does not detect the document on the sheet supply tray. Thus, there may be a case where sheet feed operation can actually be performed properly even though a setting failure is determined based on the sensor detection information. That is, there may be a case where the sensor information and actual state (i.e., whether or not the sheet feed operation can be performed) do not match each other.
In the invention disclosed in above Jpn. Pat. Appln. Laid-Open Publication No. 2008-280153, in a case where the leading end of the set document does not reach a sensor position at which it is determined that the document can be fed, an aligning means (aligning plate) is used to align the document leading end. Thus, trouble of issuing a re-set request or detecting the document set state once again can be avoided. However, providing such an aligning means requires a design change or increases production cost and a product size.
An object of the present invention is therefore to provide a sheet feeder capable of reducing occurrence of reprocessing and reoperation due to mismatch between the detection information from various detection sensors and an actual sheet set state.